Bulk acoustic wave/film bulk acoustic wave resonator and filter for wide bandwidth applications

ABSTRACT

A ladder filter comprises a plurality of series arm bulk acoustic wave resonators electrically connected in series between an input port and an output port of the ladder filter and a plurality of shunt bulk acoustic wave resonators electrically connected in parallel between adjacent ones of the plurality of series arm bulk acoustic wave resonators and ground, at least one of the plurality of shunt bulk acoustic wave resonators including raised frame regions having a first width, at least one of the plurality of series arm bulk acoustic wave resonators having one of raised frame regions having a second width less than the first width or lacking raised frame regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 as aContinuation-In-Part of U.S. patent application Ser. No. 16/881,285,filed May 22, 2020, titled “BULK ACOUSTIC WAVE/FILM BULK ACOUSTIC WAVERESONATOR AND FILTER FOR WIDE BANDWIDTH APPLICATIONS”, which claimspriority under 35 U.S.C. § 119 (e) to U.S. Provisional PatentApplication Ser. No. 62/885,454, filed Aug. 12, 2019 and to U.S.Provisional Patent Application Ser. No. 62/852,831, filed May 24, 2019,each of which being incorporated herein in its entirety for allpurposes.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices andstructures and methods of mitigating spurious signals in same.

Description of Related Technology

Acoustic wave devices, for example, bulk acoustic wave (BAW) devices maybe utilized as components of filters in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. Two acoustic wavefilters can be arranged as a duplexer.

SUMMARY

In accordance with an aspect, there is provided a ladder filter. Theladder filter comprises an input port and an output port, a plurality ofseries arm bulk acoustic wave resonators electrically connected inseries between the input port and the output port; and a plurality ofshunt bulk acoustic wave resonators connected in parallel, each of theshunt bulk acoustic wave resonators being electrically connected betweenrespective adjacent ones of the plurality of series arm bulk acousticwave resonators and ground, at least one of the plurality of shunt bulkacoustic wave resonators including a raised frame region having a firstwidth, and at least one of the plurality of series arm bulk acousticwave resonators lacking any raised frame region to thereby increase abandpass relative to filtering functionality.

In some embodiments, the plurality of series arm bulk acoustic waveresonators are each film bulk acoustic wave resonators.

In some embodiments, the plurality of shunt bulk acoustic waveresonators are each film bulk acoustic wave resonators.

In some embodiments, each of the plurality of series arm film bulkacoustic wave resonators and each of the plurality of shunt film bulkacoustic wave resonators include a piezoelectric film disposed in acentral region defining a main active domain in which a main acousticwave is generated during operation, and in a recessed frame regioncircumscribing the central region.

In some embodiments, each of the plurality of shunt film bulk acousticwave resonators include a raised frame region disposed on opposite sidesof the recessed frame region from the central region.

In some embodiments, the raised frame region of each of the plurality ofshunt film bulk acoustic wave resonators have approximately a samewidth.

In some embodiments, at least one of the plurality of shunt film bulkacoustic wave resonators has a raised frame region with a width lessthan a width of raised frame regions of others of the plurality of shuntfilm bulk acoustic wave resonators.

In some embodiments, each of the plurality of series arm film bulkacoustic wave resonators lack raised frame regions.

In some embodiments, each of the plurality of series arm film bulkacoustic wave resonators have a same resonant frequency.

In some embodiments, each of the plurality of shunt film bulk acousticwave resonators have a resonant frequency below the resonant frequencyof each of the plurality of series arm film bulk acoustic waveresonators.

In some embodiments, at least one of the plurality of shunt film bulkacoustic wave resonators has a first resonant frequency different fromresonant frequencies of others of the plurality of shunt film bulkacoustic wave resonators.

In some embodiments, at least one of the plurality of shunt film bulkacoustic wave resonators has a second resonant frequency different fromthe first resonant frequency and different from the resonant frequenciesof others of the plurality of shunt film bulk acoustic wave resonators.

In some embodiments, the ladder filter exhibits a greater insertion lossat an upper end of a passband of the ladder filter than at a lower endof the passband of the ladder filter.

In some embodiments, the ladder filter has a passband in a radiofrequency band. The passband may be greater than about 200 MHz in width.

In some embodiments, the ladder filter exhibits a relative passbandwidth wider than 5.5%, the relative passband width being defined as thefilter bandwidth divided by the filter center frequency.

In some embodiments, plurality of series arm bulk acoustic waveresonators includes at least one solidly mounted resonator.

In some embodiments, the plurality of shunt bulk acoustic waveresonators includes at least one solidly mounted resonator.

In accordance with another aspect, there is provided a ladder filter.The ladder filter comprises an input port and an output port, aplurality of series arm bulk acoustic wave resonators electricallyconnected in series between the input port and the output port, and aplurality of shunt bulk acoustic wave resonators connected in parallel,each of the shunt bulk acoustic wave resonators being electricallyconnected between respective adjacent ones of the plurality of seriesarm bulk acoustic wave resonators and ground, at least one of theplurality of shunt bulk acoustic wave resonators including a raisedframe region having a first width, and at least one of the plurality ofseries arm bulk acoustic wave resonators including a raised frame regionhaving a second width less than the first width to thereby increase abandpass relative to filtering functionality.

In some embodiments, the plurality of series arm bulk acoustic waveresonators includes at least one film bulk acoustic wave resonator.

In some embodiments, the plurality of shunt bulk acoustic waveresonators includes at least one film bulk acoustic wave resonator.

In some embodiments, the plurality of series arm bulk acoustic waveresonators includes at least one solidly mounted resonator.

In some embodiments, the plurality of shunt bulk acoustic waveresonators includes at least one solidly mounted resonator.

In accordance with another aspect, there is provided an electronicsmodule comprising a radio frequency ladder filter. The radio frequencyladder filter includes a plurality of series arm film bulk acoustic waveresonators electrically connected in series between an input port and anoutput port of the ladder filter, and a plurality of shunt film bulkacoustic wave resonators electrically connected in parallel betweenadjacent ones of the plurality of series arm film bulk acoustic waveresonators and ground, at least one of the plurality of shunt film bulkacoustic wave resonators including a raised frame region having a firstwidth, at least one of the plurality of series arm film bulk acousticwave resonators having one of a raised frame region having a secondwidth less than the first width or lacking any raised frame region.

In accordance with another aspect, there is provided an electronicdevice comprising an electronics module including a radio frequencyladder filter. The radio frequency ladder filter includes a plurality ofseries arm film bulk acoustic wave resonators electrically connected inseries between an input port and an output port of the ladder filter,and a plurality of shunt film bulk acoustic wave resonators electricallyconnected in parallel between adjacent ones of the plurality of seriesarm film bulk acoustic wave resonators and ground, at least one of theplurality of shunt film bulk acoustic wave resonators including raised aframe region having a first width, at least one of the plurality ofseries arm film bulk acoustic wave resonators having one of a raisedframe region having a second width less than the first width or lackingany raised frame region.

In accordance with another aspect, there is provided a film bulkacoustic wave resonator comprising a piezoelectric film disposed in acentral region defining a main active domain in which a main acousticwave is generated during operation, and in a recessed frame regioncircumscribing the central region, the film bulk acoustic wave resonatorlacking any raised frame region.

In accordance with another aspect, there is provided a radio frequencyfilter comprising a film bulk acoustic wave resonator including apiezoelectric film disposed in a central region defining a main activedomain in which a main acoustic wave is generated during operation, andin a recessed frame region circumscribing the central region, the filmbulk acoustic wave resonator lacking any raised frame region.

In accordance with another aspect, there is provided an electronicsmodule comprising a radio frequency filter including a film bulkacoustic wave resonator having a piezoelectric film disposed in acentral region defining a main active domain in which a main acousticwave is generated during operation, and in a recessed frame regioncircumscribing the central region, the film bulk acoustic wave resonatorlacking any raised frame region.

In accordance with another aspect, there is provided an electronicdevice comprising an electronics module including a radio frequencyfilter having a film bulk acoustic wave resonator with a piezoelectricfilm disposed in a central region defining a main active domain in whicha main acoustic wave is generated during operation, and in a recessedframe regions circumscribing the central region, the film bulk acousticwave resonator lacking any raised frame region.

In accordance with another aspect, there is provided a ladder filter.The ladder filter comprises an input port and an output port, aplurality of series arm bulk acoustic wave resonators electricallyconnected in series between the input port and the output port, oneresonator of the plurality of series arm bulk acoustic resonators havinga higher resonance frequency than a resonance frequency of at least oneother resonator of the plurality of series arm bulk acoustic resonators,the one resonator lacking any raised frame, and a plurality of shuntbulk acoustic wave resonators connected in parallel, each of the shuntbulk acoustic wave resonators being electrically connected betweenrespective adjacent ones of the plurality of series arm bulk acousticwave resonators and ground.

In some embodiments, the at least one other resonator includes a raisedframe.

In some embodiments, a second resonator of the plurality of series armbulk acoustic resonators has a higher resonance frequency than the atleast one other resonator, a lower resonance frequency that the oneresonator, and lacks any raised frame. One of the one resonator or thesecond resonator may lack any recessed frame. Each of the one resonatorand the second resonator may lack any recessed frame. Each of theplurality of series arm bulk acoustic resonators other than the oneresonator and the second resonator may include a raised frame. Each ofthe plurality of series arm bulk acoustic resonators other than the oneresonator and the second resonator may include a recessed frame.

In some embodiments, each of the plurality of series arm film bulkacoustic wave resonators other than the one resonator and the secondresonator have a same resonant frequency.

In some embodiments, the plurality of series arm bulk acoustic waveresonators are each film bulk acoustic wave resonators.

In some embodiments, the ladder filter has a passband in a radiofrequency band. The passband may be greater than about 200 MHz in width.

In accordance with another aspect, there is provided a ladder filter.The ladder filter comprises an input port and an output port, aplurality of series arm bulk acoustic wave resonators electricallyconnected in series between the input port and the output port, a firstsubset of the plurality of series arm bulk acoustic wave resonatorshaving higher resonance frequencies than resonance frequencies of asecond subset of the plurality of series arm bulk acoustic waveresonators, the first subset of the plurality of series arm bulkacoustic wave resonators lacking raised frames, and a plurality of shuntbulk acoustic wave resonators connected in parallel, each of the shuntbulk acoustic wave resonators being electrically connected betweenrespective adjacent ones of the plurality of series arm bulk acousticwave resonators and ground.

In some embodiments, the second subset of the plurality of series armbulk acoustic wave resonators include raised frames. At least oneresonator of the first subset of the plurality of series arm bulkacoustic wave resonators may lack a recessed frame. Each resonator ofthe first subset of the plurality of series arm bulk acoustic waveresonators may lack a recessed frame.

In some embodiments, the plurality of series arm bulk acoustic waveresonators includes at least one film bulk acoustic wave resonator. Theplurality of shunt bulk acoustic wave resonators may include at leastone film bulk acoustic wave resonator.

In accordance with another aspect, there is provided an electronicdevice comprising an electronics module including a radio frequencyladder. The radio frequency ladder filter has a plurality of series armfilm bulk acoustic wave resonators electrically connected in seriesbetween an input port and an output port of the ladder filter, oneresonator of the plurality of series arm bulk acoustic resonators havinga higher resonance frequency than at least one other resonator of theplurality of series arm bulk acoustic resonators, the one resonatorlacking any raised frame, and a plurality of shunt film bulk acousticwave resonators electrically connected in parallel between adjacent onesof the plurality of series arm film bulk acoustic wave resonators andground.

In some embodiments, at least one other resonator of the plurality ofseries arm film bulk acoustic wave resonators includes a raised frame.

In some embodiments, the one resonator lacks any recessed frame.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of an example of a film bulk acousticwave resonator;

FIG. 2 illustrates an example of a ladder filter;

FIG. 3A is a highly schematic cross-sectional illustration of a portionof a film bulk acoustic wave resonator;

FIG. 3B illustrates curves of admittance in first portions of the filmbulk acoustic wave resonator of FIG. 3A with and without a raised frameregion;

FIG. 3C illustrates curves of admittance in another portion of the filmbulk acoustic wave resonator of FIG. 3A with and without a raised frameregion;

FIG. 4A illustrates insertion loss of a ladder filter configured asillustrated in FIG. 2 with different raised frame region widths in theseries resonators of the filter, on which is superimposed the passbandof the B41 frequency band;

FIG. 4B illustrates contributions of lateral modes and raised frames inthe series resonators of a ladder filter as illustrated in FIG. 2B tospurious signals in the admittance curve of the filter;

FIG. 4C illustrates insertion loss of a ladder filter configured asillustrated in FIG. 2 with different raised frame region widths in theseries resonators of the filter, on which is superimposed the pass bandof the B3 receive frequency band;

FIG. 5A is a cross-section of an example of a film bulk acoustic waveresonator without raised frame regions;

FIG. 5B is a cross-section of another example of a film bulk acousticwave resonator without raised frame regions;

FIGS. 6A-6F illustrate the effect on the passband of a ladder filter asillustrated in FIG. 2 with different of the series resonators includingor lacking raised frame regions;

FIG. 7 illustrates another example of a ladder filter;

FIG. 8 a cross-sectional view of an example of a film bulk acoustic waveresonator lacking a raised frame and a recessed frame;

FIG. 9A is a curve of admittance v. frequency for a first seriesresonator in the ladder filter of FIG. 7;

FIG. 9B is a curve of the real part of admittance v. frequency for thefirst series resonator in the ladder filter of FIG. 7;

FIG. 9C is a curve of quality factor v. frequency for the first seriesresonator in the ladder filter of FIG. 7;

FIG. 10A is a curve of admittance v. frequency for a second seriesresonator in the ladder filter of FIG. 7;

FIG. 10B is a curve of the real part of admittance v. frequency for thesecond series resonator in the ladder filter of FIG. 7;

FIG. 10C is a curve of quality factor v. frequency for the second seriesresonator in the ladder filter of FIG. 7;

FIG. 11A is a curve of admittance v. frequency for a third seriesresonator in the ladder filter of FIG. 7;

FIG. 11B is a curve of the real part of admittance v. frequency for thethird series resonator in the ladder filter of FIG. 7;

FIG. 11C is a curve of quality factor v. frequency for the third seriesresonator in the ladder filter of FIG. 7;

FIG. 12A is a curve of admittance v. frequency for a fourth seriesresonator in the ladder filter of FIG. 7;

FIG. 12B is a curve of the real part of admittance v. frequency for thefourth series resonator in the ladder filter of FIG. 7;

FIG. 12C is a curve of quality factor v. frequency for the fourth seriesresonator in the ladder filter of FIG. 7;

FIG. 13A is a curve of admittance v. frequency for a fifth seriesresonator in the ladder filter of FIG. 7;

FIG. 13B is a curve of the real part of admittance v. frequency for thefifth series resonator in the ladder filter of FIG. 7;

FIG. 13C is a curve of quality factor v. frequency for the fifth seriesresonator in the ladder filter of FIG. 7;

FIG. 14 is a chart of insertion loss v. frequency for the filter of FIG.7 under conditions where different of the series resonators included ordid not include raised frame regions;

FIG. 15A is a curve of admittance v. frequency for FBAR resonators asillustrated in FIG. 5A having different recessed frame widths;

FIG. 15B is a curve of the real part of admittance v. frequency for FBARresonators as illustrated in FIG. 5A having different recessed framewidths;

FIG. 15C is a curve of quality factor v. frequency for FBAR resonatorsas illustrated in FIG. 5A having different recessed frame widths;

FIG. 15D is a curve of return loss v. frequency for FBAR resonators asillustrated in FIG. 5A having different recessed frame widths;

FIG. 16 is a chart illustrating the effect on insertion loss v.frequency of the presence or absence of recessed frames in the first andthird series resonators in the filter of FIG. 7;

FIG. 17A illustrates an example of a lattice filter;

FIG. 17B illustrates frequency response of an example of lattice filter;

FIG. 18A illustrates the frequency response of series and shuntresonators in an example of a notch filter;

FIG. 18B illustrates the frequency response of a notch filter formedwith resonators including raised frame regions as compared to thefrequency response of a notch filter formed with resonators lackingraised frame regions;

FIG. 19A is a cross-sectional view of an example of a solidly mountedresonator;

FIG. 19B is a cross-sectional view of another example of a solidlymounted resonator;

FIG. 19C is a cross-sectional view of another example of a solidlymounted resonator;

FIG. 20 is a block diagram of one example of a filter module that caninclude one or more acoustic wave elements according to aspects of thepresent disclosure;

FIG. 21 is a block diagram of one example of a front-end module that caninclude one or more filter modules according to aspects of the presentdisclosure; and

FIG. 22 is a block diagram of one example of a wireless device includingthe front-end module of FIG. 21.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Film bulk acoustic wave resonators (FBARs) are a form of bulk acousticwave resonator that generally includes a film of piezoelectric materialsandwiched between a top and a bottom electrode and suspended over acavity that allows for the film of piezoelectric material to vibrate. Asignal applied across the top and bottom electrodes causes an acousticwave to be generated in and travel through the film of piezoelectricmaterial. A FBAR exhibits a frequency response to applied signals with aresonance peak determined by a thickness of the film of piezoelectricmaterial. Ideally, the only acoustic wave that would be generated in aFBAR is a main acoustic wave that would travel through the film ofpiezoelectric material in a direction perpendicular to layers ofconducting material forming the top and bottom electrodes. Thepiezoelectric material of a FBAR, however, typically has a non-zeroPoisson's ratio. Compression and relaxation of the piezoelectricmaterial associated with passage of the main acoustic wave may thuscause compression and relaxation of the piezoelectric material in adirection perpendicular to the direction of propagation of the mainacoustic wave. The compression and relaxation of the piezoelectricmaterial in the direction perpendicular to the direction of propagationof the main acoustic wave may generate transverse acoustic waves thattravel perpendicular to the main acoustic wave (parallel to the surfacesof the electrode films) through the piezoelectric material. Thetransverse acoustic waves may be reflected back into an area in whichthe main acoustic wave propagates and may induce spurious acoustic wavestravelling in the same direction as the main acoustic wave. Thesespurious acoustic waves may degrade the frequency response of the FBARfrom what is expected or from what is intended and are generallyconsidered undesirable.

FIG. 1 is cross-sectional view of an example of a FBAR, indicatedgenerally at 100. The FBAR 100 is disposed on a substrate 110, forexample, a silicon substrate that may include a dielectric surface layer110A of, for example, silicon dioxide. The FBAR 100 includes a layer orfilm of piezoelectric material 115, for example, aluminum nitride (AlN).A top electrode 120 is disposed on top of a portion of the layer or filmof piezoelectric material 115 and a bottom electrode 125 is disposed onthe bottom of a portion of the layer or film of piezoelectric material115. The top electrode 120 may be formed of, for example, ruthenium(Ru). The bottom electrode 125 may include a layer 125A of Ru disposedin contact with the bottom of the portion of the layer or film ofpiezoelectric material 115 and a layer 125B of titanium (Ti) disposed ona lower side of the layer 125A of Ru opposite a side of the layer 125Aof Ru in contact with the bottom of the portion of the layer or film ofpiezoelectric material 115. Each of the top electrode 120 and the bottomelectrode 125 may be covered with a layer of dielectric material 130,for example, silicon dioxide. A cavity 135 is defined beneath the layerof dielectric material 130 covering the bottom electrode 125 and thesurface layer 110A of the substrate 110. A bottom electrical contact 140formed of, for example, copper may make electrical connection with thebottom electrode 125 and a top electrical contact 145 formed of, forexample, copper may make electrical connection with the top electrode120.

The FBAR 100 may include a central region 150 including a main activedomain in the layer or film of piezoelectric material 115 in which amain acoustic wave is excited during operation. A recessed frame regionor regions 155 may bound and define the lateral extent of the centralregion 150. The recessed frame region(s) 155 may be defined by areasthat have a thinner layer of dielectric material 130 on top of the topelectrode 120 than in the central region 150. The dielectric materiallayer 130 in the recessed frame region(s) 155 may be from about 10 nm toabout 100 nm thinner than the dielectric material layer 130 in thecentral region 150 and/or the difference in thickness of the dielectricmaterial in the recessed frame region(s) 155 vs. in the central region150 may cause the resonant frequency of the device in the recessed frameregion(s) 155 to be between about 5 MHz to about 50 MHz higher than theresonant frequency of the device in the central region 150. A raisedframe region or regions 160 may be defined on an opposite side of therecessed frame region(s) 155 from the central region 150 and maydirectly abut the outside edge(s) of the recessed frame region(s) 155.The raised frame region(s) 160 may be defined by areas where the topelectrode 120 is thicker than in the central region 150 and in therecessed frame region(s) 155. The top electrode 120 may have the samethickness in the central region 150 and in the recessed frame region(s)155 but a greater thickness in the raised frame region(s) 160. The topelectrode 120 may be between about 50 nm and about 500 nm thicker in theraised frame region(s) 160 than in the central region 150 and/or in therecessed frame region(s) 155. The raised frame region(s) may be, forexample, 4 μm or more in width.

The recessed frame region(s) 155 and the raised frame region(s) 160 maycontribute to dissipation or scattering of transverse acoustic wavesgenerated in the FBAR 100 during operation and/or may reflect transversewaves propagating outside of the recessed frame region(s) 155 and theraised frame region(s) 160 and prevent these transverse acoustic wavesfrom entering the central region and inducing spurious signals in themain active domain region of the FBAR. Without being bound to aparticular theory, it is believed that due to the thinner layer ofdielectric material 130 on top of the top electrode 120 in the recessedframe region(s) 155, the recessed frame region(s) 155 may exhibit ahigher velocity of propagation of acoustic waves than the central region150. Conversely, due to the increased thickness and mass of the topelectrode 120 in the raised frame region(s) 160, the raised frameregions(s) 160 may exhibit a lower velocity of propagation of acousticwaves than the central region 150 and a lower velocity of propagation ofacoustic waves than the recessed frame region(s) 155. The discontinuityin acoustic wave velocity between the recessed frame region(s) 155 andthe raised frame region(s) 160 creates a barrier that scatters,suppresses, and/or reflects transverse acoustic waves.

It should be appreciated that the FBAR illustrated in FIG. 1 and theFBARs and other structures illustrated in the other figures accompanyingthis disclosure are illustrated in a highly simplified form. Therelative dimensions of the different features are not shown to scale.Further, embodiments of FBARs may include additional features or layersnot illustrated or may lack one or more features or layers illustratedherein.

FBARs or other acoustic wave resonators may be combined to form a filterstructure that may operate in the radio frequency (RF) band. One type ofan acoustic wave resonator-based RF filter is known as a ladder filter.One example of a ladder filter is illustrated in FIG. 2A. The filter ofFIG. 2A includes a plurality of acoustic wave resonators R1, R2, R3, R4,R5, R6, R7, R8, R9, R10, and R11 disposed in a series arm between aninput port (IN) and an output port (OUT). Resonators R1, R3, R5, R7, R9,and R11 are connected in series between the input port and output port.Resonators R2, R4, R6, R8, and R10 are connected in parallel betweenresonators R1, R3, R5, R7, and R9 and ground. Resonators R2, R4, R6, R8,and R10 may also be referred to as shunt resonators. In someembodiments, each of the series resonators R1, R3, R5, R7, R9, and R11may have the same resonant frequency. In some embodiments, each of theplurality of shunt resonators R2, R4, R6, R8, and R10 have a resonantfrequency below the resonant frequency of each of the series armresonators R1, R3, R5, R7, and R9, and R11. At least one of theplurality of shunt resonators R2, R4, R6, R8, and R10 may have a firstresonant frequency different from resonant frequencies of others of theplurality of shunt resonators. At least one of the plurality of shuntresonators R2, R4, R6, R8, and R10 may have a second resonant frequencydifferent from the first resonant frequency and different from theresonant frequencies of others of the plurality of shunt resonators.

For ultrawide bandwidth filter implementations, for example, B41 fullband (2496 MHz-2690 MHz, a 7.5% relative bandwidth RBW), because thefilter passband is so wide, the series resonators in a ladder filter forsuch implementations should desirably exhibit high admittance (e.g., theY21 filter parameter) not only at the resonant frequency of the seriesresonators fs, but also at frequencies below, for example, 100 MHz, 120MHz, or more below fs. A ladder filter as disclosed herein may have anRBW wider than 5.5% or wider than 7.5% to facilitate use in ultrawidebandwidth filter implementations. Typical FBAR resonators, for example,as illustrated in FIG. 1 may exhibit a degradation in admittance that islarger than desirable at frequencies below, for example, 100 MHz or morebelow fs and may thus not provide optimal functionality for filtersintended for use in ultrawide bandwidth implementations, for example,for filters for the B41 full band. It has been discovered that theraised frame structure in a conventional FBAR may help increase thequality factor Q of the resonator but may degrade the admittance of theresonator at frequencies below fs of the resonator. A conventionalraised frame structure may improve Y21 performance close to the fs of aFBAR, but not in a frequency range 100 MHz or more lower than the fs ofthe FBAR.

It has been found that spurious signals in the admittance of a FBARincluding a raised frame region may be generated in the raised frameregion. In one example, the admittance curves of an example FBAR weresimulated at measurement locations TE1, TE2, and TE3 in the centralregion 150, recessed frame region 155, and raised frame region 160,respectively, as illustrated in FIG. 3A. In FIG. 3A upper region 30represents a region including frames and may include the top electrode120 and top dielectric material layer 130. Lower region 31 represents aregion of the FBAR not including frames and may include film ofpiezoelectric material 115 and bottom electrode 125. The simulatedexample FBAR exhibited spurious signals below the resonant frequency,for example, from about 2.5 GHz to about 2.6 GHz in the central region150 and recessed frame region 155 that increased in amplitude as thewidth of the recessed frame region was increased from 3 μm to 5 μm asillustrated in FIG. 3B. A secondary admittance peak also appeared abovethe resonant frequency of the FBAR as the width of the recessed frameregion was increased from 3 μm to 5 μm. As illustrated in the FIG. 3C,in the raised frame region 160, spurious signals in the admittanceappeared from about 2 GHz to just below the resonant frequency (about2.63 GHz) when a raised frame region with a width of 4 μm was present.These spurious signals were substantially suppressed when the FBAR wassimulated with no raised frame region (raised frame region width=0 μm),although some spurious signals appeared above the resonant frequency inthe FBAR with no raised frame region. The spurious signals above theresonant frequency in the FBAR with no raised frame region were lower inamplitude than the spurious signals below the resonant frequency in thesimulated FBAR with the raised frame region with a width of 4 μm.

FIG. 4A is a chart that illustrates the effect on insertion loss IL oradmittance for a filter similar to that illustrated in FIG. 2 in whichthe B41 frequency band passband, with a low channel 130 MHz below theresonant frequency of the serial resonators, is superimposed on thechart. The WiFi frequency band is also illustrated in FIG. 4A toillustrate its proximity to the B41 frequency band. As can be seen inFIG. 4A, the insertion loss was about −50 db at the low end of the B41passband when the series resonators of the filter included raised frameregions 4 μm wide (Raf4 um res. Curve). The insertion loss at the lowend of the B41 passband decreased by a couple decibels as the raisedframe regions of the series resonators of the filter were reduced to 1μm in width (RaF1 um res. curve) and decreased further to just above −60db when the raised frame regions of the series resonators were removed(RaF0 um res. curve). At the high end of the B41 passband the insertionloss increased from about −60 db, to about −55 dB, to about −50 dB asthe width of the raised frame regions of the series resonators of thefilter were decreased from 4 μm to 1 μm to 0 μm, respectively.

It should be noted that the spurious signals in the insertion loss curvemay include contributions from both lateral mode spurious signals andspurious signals caused by the raised frame. An example of the relativecontribution of these different sources of spurious signals for an FBARwith different raised frame widths is illustrated in FIG. 4B.

Although the recessed frame widths and raised frame widths are indicatedabove as absolute lengths with dimensions of μm, the recessed framewidths and raised frame widths may alternatively be expressed asdimensionless relative widths wherein the widths are expressed as amultiple of the wavelength λ of an acoustic wave in the piezoelectricmaterial of the resonators at the resonant frequency of the mainvibrational mode of the resonator.

In a comparative example, FIG. 4C is a chart that illustrates the effecton insertion loss IL or admittance for a filter similar to thatillustrated in FIG. 2 in which the B3Rx frequency band passband, with alow channel 60 MHz below the resonant frequency of the serialresonators, is superimposed on the chart. In this comparative example,changing the width of the raised frame regions of the series resonatorsof the filter has a negligible effect on insertion loss at the low endof the passband, although the insertion loss at the upper end of thepassband increases. This illustrates why it is more important to reducethe width of, or eliminate, the raised frame regions of seriesresonators in ladder filters for ultrahigh bandwidth implementationsrather than lower bandwidth implementations.

FIG. 5A illustrates a cross section of a FBAR similar to that of FIG. 1,but with the raised frame regions 160 removed (RaF=0 μm). Indicators 160are still illustrated in FIG. 5A to show where the raised frame regionswere present in the FBAR illustrated in FIG. 1. As can be seen bycomparing the FBAR structure of FIG. 1 to that FBAR structure of FIG.5A, the raised regions of the top electrode 120 in regions 160 have beenremoved in the FBAR structure of FIG. 5A. The top electrode 120 may havea substantially or fully same thickness throughout regions 150, 155, and160 in the FBAR without raised frame regions illustrated in FIG. 5A. Thesilicon dioxide layer 130 may have the same thickness in regions 150 and160 as illustrated in FIG. 5A, or alternatively, may have the samethickness in regions 155 and 160, that is thinner than the thickness inregion 150, as illustrated in FIG. 5B.

In some implementations, only a subset of the series resonators in aladder filter may lack raised frame regions. FIGS. 6A-6F illustrates howthe passband of a filter configured as illustrated in FIG. 2 changes asdifferent series resonators are configured to include raised frameregions with widths of 1 μm. As can be seen in these figures, as moreseries resonators are provided with raised frame regions, the insertionloss at the lower end of the passband decreases, but the insertion lossat the upper end of the passband increases. One may select a suitablenumber of series resonators in a ladder filter to include and to notinclude raised frame regions to achieve a passband having a desiredshape. For example, as illustrated in FIG. 6D, providing seriesresonators R1, R3, R5, and R7 with raised frame regions 1 μm in widthwhile the remainder of the series resonators lack raised frame regions,the insertion loss at the upper and lower sides of the passband areapproximately equal.

Applicants have appreciated that the bandwidth of a ladder filter may beincreased by including series resonators with different resonancefrequencies in the filter. For example, for a ladder filter includingfive series resonators S1-S5 and four parallel or shunt resonators P1-P4as illustrated in FIG. 7, the different series resonators may have thefollowing resonance frequencies:

Resonance Frequency Resonator (MHz) S1 2629 S2 2606 S3 2657 S4 2606 S52606

The admittance characteristics of the series resonators in the ladderfilter of FIG. 7 with the highest resonance frequencies will have alarger impact on the insertion loss at the lower end and middle of thepassband of the ladder filter than series resonators having lowerresonance frequencies. The admittance characteristics of the seriesresonators in the ladder filter of FIG. 7 with the highest resonancefrequencies will have a lesser impact on the insertion loss at the highend of the passband of the ladder filter than series resonators havinglower resonance frequencies. Accordingly, to reduce the insertion lossat the low end and mid-levels of the passband of the ladder filter, andincrease the bandwidth of the ladder filter while minimizing theinsertion loss change at the high end of the passband, the seriesresonator or series resonators with the highest or highest and secondhighest resonance frequencies may be formed without raised frame regions(RaW=0 μm). Additionally, for series resonators in which the raisedframe regions are eliminated, the width of the recessed frame regionsmay be adjusted to further optimize the admittance characteristics ofthe series resonators. In some embodiments, both the raised frame andthe recessed frame may be wholly omitted as illustrated in the FBAR ofFIG. 8 in which the same reference numbers refer to the same features asin the FBARs of FIGS. 2, 5A, and 5B.

The ladder filter of FIG. 7 was modeled with the series resonatorshaving the resonant frequencies listed above, with the series resonatorsS2, S4, and S5 having raised frames formed of either silicon dioxide orof metal of the upper electrode with widths of 0.8 μm (RaW=0.8 μm) andrecessed frames having widths of 1.6 μm (ReW=1.6 μm). The shuntresonators P1-P4 were modeled as having raised frames formed of eithersilicon dioxide with widths of 1 μm (RaW=1 μm) or of metal of the upperelectrode with widths of 1.9 μm (RaW=1.9 μm) and no recessed frames(ReW=0 μm). FIGS. 9A-9C, 10A-10C, 11-A-11C, 12A-12C, and 13A-13Cillustrate admittance curves, real part of admittance (conductance)curves, and quality factor curves, respectively for the seriesresonators S1 (FIGS. 9A-9C), S2 (FIGS. 10A-10C), S3 (FIGS. 11A-11C), S4(FIGS. 12A-12C), and S5 (FIGS. 13A-13C) of the FBAR of FIG. 7. Thecharts for resonators S3 (the series resonator with highest resonancefrequency) and S1 (the series resonator with second highest frequency)include curves for these resonators including raised frame regions (theRaW curves), curves for these resonators lacking raised frame regionsand lacking recessed frame regions (the RaW=0, ReW=0 curves), and curvesfor these resonators lacking a raised frame regions but including 3.2 μmwide recessed frame regions (the RaW=0, ReW=3.2 μm curves).

As can be observed in FIGS. 9A-9C with reference to resonator S1 andFIGS. 11A-11C with respect to resonator S3, the real part of theadmittance of both of resonators S1 and S3 decreased at a frequency of2.496 GHz, corresponding to a lower edge of the B41 frequency bandpassband when the raised frame was eliminated from these resonators andunder conditions in which the recessed frame was also eliminated or not.At a frequency of 2.69 GHz, corresponding to the upper edge of the B41frequency band passband the real impedance of both the S1 and S3resonators increased when the raised frame was eliminated from theseresonators and under conditions in which the recessed frame was alsoeliminated or not. This increase in the real part of admittance at theupper edge of the B41 frequency band passband corresponded with areduction in sharpness of the antiresonance peak in the admittancecurves for these resonators. The elimination of the raised frame fromresonators S1 and S3 also decreased the quality factor of theseresonators, most significantly at frequencies close to or above theupper edge of the B41 frequency band passband.

FIG. 14 illustrates insertion loss of a ladder filter configured asillustrated in FIG. 7 under the base case condition in which all of theseries resonators included raised frame regions 0.8 μm wide and recessedframe regions 1.6 μm wide (the RaW curve), under the condition in whichthe S3 resonator had no raised frame region and a recessed frame regionwith a width of 3.2 μm (the S3 RaW=0 curve), and under the condition inwhich both the S3 and S1 resonators had no raised frame regions andrecessed frame regions with widths of 3.2 μm (the S1/S3 RaW=0 curve).Under the condition where all of the series resonators included raisedframe regions and recessed frame regions, the insertion loss at afrequency of 2.496 GHz, corresponding to a lower edge of the B41frequency band passband, was −3.344 dB and the insertion loss at afrequency of 2.69 GHz, corresponding to the upper edge of the B41frequency band passband, was −2.325 dB. Under the condition in which theS3 resonator had no raised frame region and a recessed frame region witha width of 3.2 μm the insertion loss at 2.496 GHz was −3.25 dB and theinsertion loss at 2.69 GHz was −2.344 dB. Under the condition in whichboth the S3 and S1 resonators had no raised frame regions and recessedframe regions with widths of 3.2 μm the insertion loss at 2.496 GHz was−3.203 dB and the insertion loss at 2.69 GHz was −2.454 dB. Accordinglythe insertion loss at the lower end of the passband was improvedalthough the upper end of the passband was slightly degraded under thecondition in which the S3 resonator had no raised frame region and arecessed frame region with a width of 3.2 μm as compared to the basecase. The insertion loss at the lower end of the passband was furtherimproved under the condition in which both the S3 and S1 resonators hadno raised frame regions and recessed frame regions with widths of 3.2 μmas compared with the base case, but the insertion loss at the upper endof the passband was further degraded.

Simulations were also performed to examine the effect of recessed framewidth on performance characteristics of a FBAR resonator such asillustrated in FIG. 5A having no raised frame region. Charts ofadmittance, real admittance (conductance), quality factor, and returnloss for FBAR resonators such as illustrated in FIG. 5A having no raisedframe region and recessed frame regions with widths ranging from 0 μm(no recessed frame region) to 3.2 μm are illustrated in FIGS. 15A-15D,respectively. All simulated performance characteristics, includinginsertion loss at the lower and mid-level frequencies of the B41frequency band, generally improved with increasing recessed frame width,although for the largest recessed frame widths spurious signals began toappear in the conductance curves above the 2.69 GHz upper edge of theB41 passband. These spurious signals are considered undesirable and thusit may be desired to limit the recessed frame width to no more thanabout 3.2 μm in FBAR resonators having no raised frame widths asdisclosed herein.

The impact on insertion loss of the presence of a recessed frame (widthof 3.2 μm) v. the absence of a recessed frame in series resonators S1and S3 having no raised frames in a ladder filter as illustrated in FIG.7 in which the other series resonators each included raised frames andrecessed frames was also evaluated. The results of this simulation areillustrated in FIG. 16. Insertion loss at both the lower (2.496 GHz) andupper (2.69 GHz) ends of the B41 passband was approximately the same forconditions under which the S1 and S3 resonators included recessed frameregions or did not. The insertion loss at frequencies in the middle ofthe passband, for example, at about 2.6 GHz was improved under thecondition where the S1 and S3 resonators included recessed frame regionsv. the condition in which they did not.

Resonators as disclosed herein may be utilized not only in ladderfilters, but also in other forms of filters, for example, latticefilters or band rejection/notch filters. One example of a lattice filterconfiguration is illustrated in FIG. 17A. An example of frequencyresponse of a lattice filter is illustrated in FIG. 17B. In examples oflattice filters or notch filters disclosed herein, each of theresonators in a filter may be formed without raised frame regions, forexample, in implementations in which it is important to minimizeinsertion loss at the lower side of the passband. In otherimplementations, the parallel resonators (Y_(e) for the lattice filterillustrated in FIG. 17A) may include raised frame regions, but one ormore of the series resonators (Y_(o) for the lattice filter illustratedin FIG. 17A) may be formed without raised frame regions, for example, inimplementations in which it is important to minimize insertion loss atthe upper side of the passband.

The frequency response and relative locations of the resonant frequencyfor series resonators (f_(SE_res)), anti-resonant frequency for seriesresonators (f_(SE_antires)), resonant frequency for shunt resonators(f_(SH_res)), and anti-resonant frequency for shunt resonators(f_(SE_antires)) in an example of a notch filter are illustrated in FIG.18A. A comparison between the frequency responses of a notch filterutilizing resonators with raised frame regions and without raised frameregions is illustrated in FIG. 18B. It can be seen that a notch filterformed with resonators including raised frame regions may have a sharpernotch than a notch filter formed with resonators lacking includingraised frame regions, but at the expense of a slightly lower admittanceat frequencies below the notch.

Although bulk acoustic wave resonators in the form of film bulk acousticwave resonators have been discussed above, it is to be appreciated thataspects and embodiments of filters as disclosed herein may include oneor more bulk acoustic wave resonators in the form of a solidly mountedresonator (SMR). In some embodiments, a filter, for example a radiofrequency ladder filter, may include only SMRs and no FBARs or acombination of SMRs and FBARs. One or more of the SMRs as disclosedherein that may be used in a filter may include a raised frame, forexample, as illustrated in FIGS. 19A and 19B, or may have a raised framewith a lesser width or height than other SMRs used in a filter, or noraised frame at all, for example, as illustrated in FIG. 19C. Asillustrated in FIGS. 19A-19C embodiments of SMRs disclosed herein mayinclude a piezoelectric layer formed of, for example, aluminum nitrideor another suitable piezoelectric material, an upper electrode (themetal 2 layer in FIGS. 19A-19C) disposed on an upper surface of thepiezoelectric layer, and a lower electrode (the metal 1 layer in FIGS.19A-19C) disposed on lower surface of the piezoelectric layer. Thepiezoelectric layer and upper and lower electrodes may be disposed on aBragg reflector formed of alternating layers of a first material with ahigh acoustic impedance, for example, tungsten, and a second materialwith a lower acoustic impedance than the first material, for example,SiO₂. The Bragg reflector may be mounted on a substrate, for example, asilicon substrate. In SMRs including a raised frame, the raised framemay include a layer of a dielectric material, for example, SiO₂ disposedon an upper surface of the upper electrode (the RaF 2 layer illustratedin FIGS. 19A and 19B) in a raised frame domain region of the resonator.Additionally or alternatively, the raised frame may include a layer of adielectric material, for example, SiO₂ (the RaF 1 layer illustrated inFIG. 19B) disposed between the lower surface of the upper electrode andthe piezoelectric material in a raised frame domain region of theresonator.

The acoustic wave devices discussed herein can be implemented in avariety of packaged modules. Some example packaged modules will now bediscussed in which any suitable principles and advantages of thepackaged acoustic wave devices discussed herein can be implemented.FIGS. 20, 21, and 22 are schematic block diagrams of illustrativepackaged modules and devices according to certain embodiments.

As discussed above, embodiments of the disclosed BAW resonators can beconfigured as or used in filters, for example. In turn, a BAW filterusing one or more BAW resonator elements may be incorporated into andpackaged as a module that may ultimately be used in an electronicdevice, such as a wireless communications device, for example. FIG. 20is a block diagram illustrating one example of a module 700 including aBAW filter 710. The BAW filter 710 may be implemented on one or moredie(s) 720 including one or more connection pads 722. For example, theBAW filter 710 may include a connection pad 722 that corresponds to aninput contact for the BAW filter and another connection pad 722 thatcorresponds to an output contact for the BAW filter. The packaged module700 includes a packaging substrate 730 that is configured to receive aplurality of components, including the die 720. A plurality ofconnection pads 732 can be disposed on the packaging substrate 730, andthe various connection pads 722 of the BAW filter die 720 can beconnected to the connection pads 732 on the packaging substrate 730 viaelectrical connectors 734, which can be solder bumps or wirebonds, forexample, to allow for passing of various signals to and from the BAWfilter 710. The module 700 may optionally further include othercircuitry die 740, such as, for example one or more additionalfilter(s), amplifiers, pre-filters, modulators, demodulators, downconverters, and the like, as would be known to one of skill in the artof semiconductor fabrication in view of the disclosure herein. In someembodiments, the module 700 can also include one or more packagingstructures to, for example, provide protection and facilitate easierhandling of the module 700. Such a packaging structure can include anovermold formed over the packaging substrate 730 and dimensioned tosubstantially encapsulate the various circuits and components thereon.

Various examples and embodiments of the BAW filter 710 can be used in awide variety of electronic devices. For example, the BAW filter 710 canbe used in an antenna duplexer, which itself can be incorporated into avariety of electronic devices, such as RF front-end modules andcommunication devices.

Referring to FIG. 20, there is illustrated a block diagram of oneexample of a front-end module 800, which may be used in an electronicdevice such as a wireless communications device (e.g., a mobile phone)for example. The front-end module 800 includes an antenna duplexer 810having a common node 802, an input node 804, and an output node 806. Anantenna 910 is connected to the common node 802.

The antenna duplexer 810 may include one or more transmission filters812 connected between the input node 804 and the common node 802, andone or more reception filters 814 connected between the common node 802and the output node 806. The passband(s) of the transmission filter(s)are different from the passband(s) of the reception filters. Examples ofthe BAW filter 710 can be used to form the transmission filter(s) 812and/or the reception filter(s) 814. An inductor or other matchingcomponent 820 may be connected at the common node 802.

The front-end module 800 further includes a transmitter circuit 832connected to the input node 804 of the duplexer 810 and a receivercircuit 834 connected to the output node 806 of the duplexer 810. Thetransmitter circuit 832 can generate signals for transmission via theantenna 910, and the receiver circuit 834 can receive and processsignals received via the antenna 910. In some embodiments, the receiverand transmitter circuits are implemented as separate components, asshown in FIG. 21, however in other embodiments these components may beintegrated into a common transceiver circuit or module. As will beappreciated by those skilled in the art, the front-end module 800 mayinclude other components that are not illustrated in FIG. 21 including,but not limited to, switches, electromagnetic couplers, amplifiers,processors, and the like.

FIG. 22 is a block diagram of one example of a wireless device 900including the antenna duplexer 810 shown in FIG. 21. The wireless device900 can be a cellular phone, smart phone, tablet, modem, communicationnetwork or any other portable or non-portable device configured forvoice or data communication. The wireless device 900 can receive andtransmit signals from the antenna 910. The wireless device includes anembodiment of a front-end module 800 similar to that discussed abovewith reference to FIG. 21. The front-end module 800 includes theduplexer 810, as discussed above. In the example shown in FIG. 22 thefront-end module 800 further includes an antenna switch 840, which canbe configured to switch between different frequency bands or modes, suchas transmit and receive modes, for example. In the example illustratedin FIG. 22, the antenna switch 840 is positioned between the duplexer810 and the antenna 910; however, in other examples the duplexer 810 canbe positioned between the antenna switch 840 and the antenna 910. Inother examples the antenna switch 840 and the duplexer 810 can beintegrated into a single component.

The front-end module 800 includes a transceiver 830 that is configuredto generate signals for transmission or to process received signals. Thetransceiver 830 can include the transmitter circuit 832, which can beconnected to the input node 804 of the duplexer 810, and the receivercircuit 834, which can be connected to the output node 806 of theduplexer 810, as shown in the example of FIG. 21.

Signals generated for transmission by the transmitter circuit 832 arereceived by a power amplifier (PA) module 850, which amplifies thegenerated signals from the transceiver 830. The power amplifier module850 can include one or more power amplifiers. The power amplifier module850 can be used to amplify a wide variety of RF or other frequency-bandtransmission signals. For example, the power amplifier module 850 canreceive an enable signal that can be used to pulse the output of thepower amplifier to aid in transmitting a wireless local area network(WLAN) signal or any other suitable pulsed signal. The power amplifiermodule 850 can be configured to amplify any of a variety of types ofsignal, including, for example, a Global System for Mobile (GSM) signal,a code division multiple access (CDMA) signal, a W-CDMA signal, aLong-Term Evolution (LTE) signal, or an EDGE signal. In certainembodiments, the power amplifier module 850 and associated componentsincluding switches and the like can be fabricated on gallium arsenide(GaAs) substrates using, for example, high-electron mobility transistors(pHEMT) or insulated-gate bipolar transistors (BiFET), or on a Siliconsubstrate using complementary metal-oxide semiconductor (CMOS) fieldeffect transistors.

Still referring to FIG. 22, the front-end module 800 may further includea low noise amplifier module 860, which amplifies received signals fromthe antenna 910 and provides the amplified signals to the receivercircuit 834 of the transceiver 830.

The wireless device 900 of FIG. 22 further includes a power managementsub-system 920 that is connected to the transceiver 830 and manages thepower for the operation of the wireless device 900. The power managementsystem 920 can also control the operation of a baseband sub-system 930and various other components of the wireless device 900. The powermanagement system 920 can include, or can be connected to, a battery(not shown) that supplies power for the various components of thewireless device 900. The power management system 920 can further includeone or more processors or controllers that can control the transmissionof signals, for example. In one embodiment, the baseband sub-system 930is connected to a user interface 940 to facilitate various input andoutput of voice and/or data provided to and received from the user. Thebaseband sub-system 930 can also be connected to memory 950 that isconfigured to store data and/or instructions to facilitate the operationof the wireless device, and/or to provide storage of information for theuser. Any of the embodiments described above can be implemented inassociation with mobile devices such as cellular handsets. Theprinciples and advantages of the embodiments can be used for any systemsor apparatus, such as any uplink wireless communication device, thatcould benefit from any of the embodiments described herein. Theteachings herein are applicable to a variety of systems. Although thisdisclosure includes some example embodiments, the teachings describedherein can be applied to a variety of structures. Any of the principlesand advantages discussed herein can be implemented in association withRF circuits configured to process signals in a range from about 30 kHzto 300 GHz, such as in a range from about 450 MHz to 6 GHz.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as packaged radio frequency modules, uplinkwireless communication devices, wireless communication infrastructure,electronic test equipment, etc. Examples of the electronic devices caninclude, but are not limited to, a mobile phone such as a smart phone, awearable computing device such as a smart watch or an ear piece, atelephone, a television, a computer monitor, a computer, a modem, ahand-held computer, a laptop computer, a tablet computer, a microwave, arefrigerator, a vehicular electronics system such as an automotiveelectronics system, a stereo system, a digital music player, a radio, acamera such as a digital camera, a portable memory chip, a washer, adryer, a washer/dryer, a copier, a facsimile machine, a scanner, amulti-functional peripheral device, a wrist watch, a clock, etc.Further, the electronic devices can include unfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” and words of similar import, when usedin this application, shall refer to this application as a whole and notto any particular portions of this application. Where the contextpermits, words in the above Detailed Description using the singular orplural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

What is claimed is:
 1. A ladder filter comprising: an input port and anoutput port; a plurality of series arm bulk acoustic wave resonatorselectrically connected in series between the input port and the outputport, one resonator of the plurality of series arm bulk acousticresonators having a higher resonance frequency than a resonancefrequency of at least one other resonator of the plurality of series armbulk acoustic resonators, the one resonator lacking any raised frame;and a plurality of shunt bulk acoustic wave resonators connected inparallel, each of the shunt bulk acoustic wave resonators beingelectrically connected between respective adjacent ones of the pluralityof series arm bulk acoustic wave resonators and ground.
 2. The ladderfilter of claim 1 wherein the at least one other resonator includes araised frame.
 3. The ladder filter of claim 1 wherein a second resonatorof the plurality of series arm bulk acoustic resonators has a higherresonance frequency than the at least one other resonator, a lowerresonance frequency that the one resonator, and lacks any raised frame.4. The ladder filter of claim 3 wherein one of the one resonator or thesecond resonator lacks any recessed frame.
 5. The ladder filter of claim3 wherein each of the one resonator and the second resonator lacks anyrecessed frame.
 6. The ladder filter of claim 3 wherein each of theplurality of series arm bulk acoustic resonators other than the oneresonator and the second resonator includes a raised frame.
 7. Theladder filter of claim 6 wherein each of the plurality of series armbulk acoustic resonators other than the one resonator and the secondresonator include a recessed frame.
 8. The ladder filter of claim 3wherein each of the plurality of series arm film bulk acoustic waveresonators other than the one resonator and the second resonator have asame resonant frequency.
 9. The ladder filter of claim 1 wherein theplurality of series arm bulk acoustic wave resonators are each film bulkacoustic wave resonators.
 10. The ladder filter of claim 1 having apassband in a radio frequency band.
 11. The ladder filter of claim 10wherein the passband is greater than about 200 MHz in width.
 12. Aladder filter comprising: an input port and an output port; a pluralityof series arm bulk acoustic wave resonators electrically connected inseries between the input port and the output port, a first subset of theplurality of series arm bulk acoustic wave resonators having higherresonance frequencies than resonance frequencies of a second subset ofthe plurality of series arm bulk acoustic wave resonators, the firstsubset of the plurality of series arm bulk acoustic wave resonatorslacking raised frames; and a plurality of shunt bulk acoustic waveresonators connected in parallel, each of the shunt bulk acoustic waveresonators being electrically connected between respective adjacent onesof the plurality of series arm bulk acoustic wave resonators and ground.13. The ladder filter of claim 12 wherein the second subset of theplurality of series arm bulk acoustic wave resonators include raisedframes.
 14. The ladder filter of claim 13 wherein at least one resonatorof the first subset of the plurality of series arm bulk acoustic waveresonators lacks a recessed frame.
 15. The ladder filter of claim 14wherein each resonator of the first subset of the plurality of seriesarm bulk acoustic wave resonators lacks a recessed frame.
 16. The ladderfilter of claim 12 wherein the plurality of series arm bulk acousticwave resonators includes at least one film bulk acoustic wave resonator.17. The ladder filter of claim 16 wherein the plurality of shunt bulkacoustic wave resonators includes at least one film bulk acoustic waveresonator.
 18. An electronic device comprising an electronics moduleincluding a radio frequency ladder filter having: a plurality of seriesarm film bulk acoustic wave resonators electrically connected in seriesbetween an input port and an output port of the ladder filter, oneresonator of the plurality of series arm bulk acoustic resonators havinga higher resonance frequency than at least one other resonator of theplurality of series arm bulk acoustic resonators, the one resonatorlacking any raised frame; and a plurality of shunt film bulk acousticwave resonators electrically connected in parallel between adjacent onesof the plurality of series arm film bulk acoustic wave resonators andground.
 19. The electronic device of claim 18 wherein at least one otherresonator of the plurality of series arm film bulk acoustic waveresonators includes a raised frame.
 20. The electronic device of claim18 wherein the one resonator lacks any recessed frame.